The objective of the proposed studies is to ascertain the separate and combined regulatory effects of endocrine and neural factors on the production and metabolism of calcitonin (CT) and its biosynthetic precursors--procalcitonin (proCT) and a putative prepolcalcitonin (preproCT). For these studies we will employ in vitro preparations of functional C-cells, including organ cultures, suspension cultures, and long-lived monolayer cultures. Our preliminary investigations have shown these C-cell preparations to be exceptionally well suited for regulatory studies of both production and secretion of CT. For instance, we have noted regulatory actions and interactions of enteric polypeptide hormones and vitamin D metabolites and adrenergic and cholinergic agonists on CT production and secretion. Our studies will characterize the separate and combined effects of many neural and endocrine factors on CT secretion and production. We will determine the acute and/or chronic effects of individual and combined regulatory factors on the rates of synthesis, of cleavage, and of degradation of CT, proCT, and preproCT. Relative changes in the rates of these processes will be studied by pulse, pulse-chase, and double-label radioisotopic techniques. Immunoextracted radiolabeled CT moieties chromatography. Regulatory effects on the concentrations of specific CT moieties will be assessed by radioimmunoassay. Effects on the rates of production, cleavage, and/or degradation of CT, proCT, and preproCT will be assessed by incorporation and by decay of radioactivity in specific CT moieties. Understanding the individual and combined regulatory effects of endocrine and neural factors on the rates of synthesis and proteolysis of specific CT moieties will illuminate the metabolic basis for the multifactorial regulation of polypeptide biosynthesis and secretion in eukaryotic cells.